Cameras, including automatic license plate recognition (ALPR) cameras, also known as automatic number plate recognition (ANPR) cameras, are commonly used in traffic applications. For example, such cameras can be used to detect vehicles that violate traffic signals or travel at a speed above a designated speed limit for a given road.
Average speed violations are often detected by a first camera capturing the time and license plate number of a vehicle. A second camera located a known distance from the first camera captures the time and license plate number of the vehicle as the vehicle passes the second camera. Each camera then sends the data to a back-end or remote server or processor. The remote processor can then identify which vehicles exceeded the speed limit on the area of road between the two cameras. Such a system is often referred to as an average speed detection system. U.S. patent application Ser. No. 12/146,716 to Fliegen describes such a system.
Many ALPR cameras include both infrared cameras and visible light cameras. Infrared cameras can be used to detect the number on the license plate, and visible light cameras can take photographs of the vehicle or driver to use as evidence of the violation. Illumination of the area is often used to improve image quality of the visible light camera, especially in the hours of darkness.
In other speed detection methods, specifically a point speed detection method using a radar or laser to detect speed, Xenon or light emitting diode (LED) flash illumination is a well known technique for generating good lighting conditions for capturing photographs of a passing vehicle.
Improvements to average speed detection systems would be welcomed.